Add option for downloading data as CSV or JSON

[RobertGemmaJr]

• CSV, JSON, or both?

jsontocsv for handling the data conversion

[celstark]

FWIW, I've set my app up to do both JSON and CSV. The idea being that most people will want something simple (trial by trial CSV), but that we should hang onto everything if we can (JSON) even if it's too awkward for most mere mortals ;)

[RobertGemmaJr]

The pure JSON is stored in Firestore for folks running their experiment online. We roll our own CLI script for downloading that data and are looking to add CSV support to it!